Degradation of polybenzimidazole in alkaline solution with first-principles Modeling

Membrane-based polybenzimidazole (mPBI) emerges as an exciting electrolyte membrane for alkaline fuel cells and water electrolyzers due to its useful ion conductivity range after being doped with aqueous KOH. However, the polymer degradation at highly concentrations limits practical use. Herein, density functional theory (DFT) calculations are used study mechanism of mPBI molecule in solution. The pristine deprotonates form ionized solution, predominant high pH. nucleophilic hydroxide C2 position initiates degradation, whereas formation fully deprotonated ionic suppresses attack. reaction then proceeds by ring-opening chain scission reactions. is preferred ancillary or during proton transfer process. rate-determining state transition involving amide cleavage scission. Combining implicit-explicit solvation models found stabilize intermediate states, lowering energy barrier. With one two explicit molecules, free barrier agrees well experimental lifetimes. An increase KOH concentration increases rate, agreeing experiments.